U.S. patent number 10,982,656 [Application Number 15/542,773] was granted by the patent office on 2021-04-20 for wind turbine with lightning protection system.
This patent grant is currently assigned to LM WP PATENT HOLDING A/S. The grantee listed for this patent is LM WP PATENT HOLDING A/S. Invention is credited to Knud Moller Andersen, Richard Baker, Lars Bo Hansen, Ole Kiel Jensen.
United States Patent |
10,982,656 |
Andersen , et al. |
April 20, 2021 |
Wind turbine with lightning protection system
Abstract
The present invention relates to a wind turbine comprising a
lightning protection system comprising a waveguide interconnecting
a communication device and a signal-carrying structure. In other
aspects, the present invention relates to the use of a waveguide in
a lightning protection system of a wind turbine, a power splitter
and its use in a lightning protection system of a wind turbine.
Inventors: |
Andersen; Knud Moller (Herning,
DK), Jensen; Ole Kiel (Gistrup, DK), Baker;
Richard (Lichfield, GB), Hansen; Lars Bo
(Agerskov, DK) |
Applicant: |
Name |
City |
State |
Country |
Type |
LM WP PATENT HOLDING A/S |
Kolding |
N/A |
DK |
|
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Assignee: |
LM WP PATENT HOLDING A/S
(Kolding, DK)
|
Family
ID: |
1000005499598 |
Appl.
No.: |
15/542,773 |
Filed: |
January 12, 2016 |
PCT
Filed: |
January 12, 2016 |
PCT No.: |
PCT/EP2016/050463 |
371(c)(1),(2),(4) Date: |
July 11, 2017 |
PCT
Pub. No.: |
WO2016/113249 |
PCT
Pub. Date: |
July 21, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180010583 A1 |
Jan 11, 2018 |
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Foreign Application Priority Data
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Jan 12, 2015 [EP] |
|
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15150790 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01R
4/66 (20130101); H02G 13/40 (20130101); F03D
80/30 (20160501); F03D 1/0675 (20130101); H01Q
1/50 (20130101); Y02E 10/72 (20130101) |
Current International
Class: |
F03D
80/30 (20160101); H02G 13/00 (20060101); H01R
4/66 (20060101); H01Q 1/50 (20060101); F03D
1/06 (20060101) |
Field of
Search: |
;416/146 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0633622 |
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Jan 1995 |
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EP |
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0633622 |
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Jan 1995 |
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EP |
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2014187895 |
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Nov 2014 |
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WO |
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WO-2014187895 |
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Nov 2014 |
|
WO |
|
Other References
European Search Report dated Jun. 25, 2015 corresponding to
application No. EP15150790. cited by applicant .
International Search Report dated Jun. 20, 2016 corresponding to
application No. PCT/EP2016/050463. cited by applicant .
Written Opinion of the International Searching Authority dated Jun.
20, 2016 corresponding to application No. PCT/EP2016/050463. cited
by applicant.
|
Primary Examiner: Dallo; Joseph J
Assistant Examiner: Reinbold; Scott A
Attorney, Agent or Firm: Nath, Goldberg & Meyer Meyer;
Jerald L. Harkins; Tanya E.
Claims
The invention claimed is:
1. A wind turbine comprising at least one turbine blade and a
lightning protection system, the turbine blade extending in a
longitudinal direction parallel to a longitudinal axis and having a
tip end and a root end, wherein the wind turbine comprises: at
least one communication device located within the wind turbine; at
least one antenna connected to the communication device; at least
one signal-carrying structure for transferring a signal between the
communication device and the at least one antenna; at least one
waveguide interconnecting the communication device and the
signal-carrying structure; at least one lightning receptor; and at
least one lightning down conductor connected to the lightning
receptor for conducting lightning current to the root end of the
blade for connection to a ground plane; wherein the signal-carrying
structure and the lightning down conductor are short-circuited at
one or more locations within the blade.
2. The wind turbine according to claim 1, wherein the
signal-carrying structure comprises one or more signal-carrying
coaxial cables, each coaxial cable comprising a centre conductor
surrounded by a first tubular insulating layer enclosed by a
tubular shield conductor.
3. The wind turbine according to claim 2, wherein one or more of
the signal-carrying coaxial cables is at least over part of its
length integrated into a three-conductor cable comprising a second
tubular insulating layer surrounding the tubular shield conductor,
the second tubular insulating layer being surrounded by at least
part of the lightning down conductor.
4. The wind turbine according to claim 1, wherein the
signal-carrying structure comprises at least one power splitter for
splitting and transferring radio frequency power, the power
splitter comprising one input port and at least two output ports,
each port being adapted to connectively receive a signal-carrying
cable, wherein the input port is connected to each of the output
ports such that a radio frequency signal received at the input port
is split to the output ports.
5. The wind turbine according to claim 4, wherein the power
splitter comprises a conductive housing connected to the input port
to enable a direct current short circuit of the housing and the
input port.
6. The wind turbine according to claim 4, wherein the
signal-carrying structure is short-circuited with the lightning
down conductor at the power splitter.
7. The wind turbine according to claim 4, wherein the input port
and at least one of the output ports is adapted to connectively
receive a three-conductor cable, wherein the three-conductor cable
comprises a second tubular insulating layer surrounding the tubular
shield conductor, the second tubular insulating layer being
surrounded by at least part of the lightning down conductor.
8. The wind turbine according to claim 1, wherein the blade
comprises two or more antennas placed at different longitudinal
distances to the tip end of the blade, e.g. wherein the blade
comprises a first and a second antenna, the first antenna being
placed within 1 meter longitudinal distance from the tip end of the
blade, and wherein the second antenna is placed between 4 and 10
meters longitudinal distance from the tip end of the blade.
9. The wind turbine according to claim 1, wherein the signal is a
radio frequency signal.
10. A wind turbine blade comprising a lightning protection system,
the wind turbine blade extending in a longitudinal direction
parallel to a longitudinal axis and having a tip end and a root
end, wherein the blade comprises: at least one communication device
located within the blade; at least one antenna connected to the
communication device; at least one signal-carrying structure for
transferring a signal between the communication device and the at
least one antenna; at least one waveguide interconnecting the
communication device and the signal-carrying structure; at least
one lightning receptor; and at least one lightning down conductor
connected to the lightning receptor for conducting lightning
current to the root end of the blade for connection to a ground
plane; wherein the signal-carrying structure and the lightning down
conductor are short-circuited at one or more locations within the
blade.
Description
This is a National Phase Application filed under 35 U.S.C. 371 as a
national stage of PCT/EP2016/050463, filed Jan. 12, 2016, an
application claiming the benefit of European Application No.
15150790.2, filed Jan. 12, 2015, the content of each of which is
hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates to a wind turbine comprising a
lightning protection system. In other aspects, the present
invention relates to the use of a waveguide in a lightning
protection system of a wind turbine, a power splitter and its use
in a lightning protection system of a wind turbine.
BACKGROUND OF THE INVENTION
Lightning protection of blade and blade components, especially
electronic parts, in a wind turbine blade is important in that the
lightning current may be very damaging. Therefore, blades may be
equipped with receptors receiving the lightning and down conductors
for conducting the lightning current to a ground potential. This
however may not be enough to protect electronic components located
in the blade against damage caused by a lightning current.
International Patent Application WO 2014/187895 A1 describes a
lightning protection system for a wind turbine blade, the system
comprising a conductive band positioned around the circumference of
the blade at the longitudinal location a communication device,
wherein the conductive band is coupled with a lightning down
conductor for connection to a ground plane. A signal-carrying
coaxial cable is incorporated into the interior of the lightning
down conductor in a common cable, wherein the lightning down
conductor is configured to shield the internal signal-carrying
structure.
While such prior art system may afford some degree of protection of
electronics from lightning strikes they typically provide
unsatisfactory protection against flashover of lighting current
between conductors having great differences in electric
potential.
Therefore, it is an object of the invention to provide a wind
turbine blade with a lightning protection system affording an
improved level of protection for electronic parts, especially
communication devices, located within the blade.
It is another object of the present invention to provide a wind
turbine blade with a lightning protection system having improved
performance as compared to prior art systems.
SUMMARY OF THE INVENTION
In a first aspect, the present invention relates to a wind turbine
comprising at least one turbine blade and a lightning protection
system, the turbine blade extending in a longitudinal direction
parallel to a longitudinal axis and having a tip end and a root
end, wherein the wind turbine comprises at least one communication
device located within the wind turbine; at least one antenna
connected to the communication device; at least one signal-carrying
structure for transferring a signal between the communication
device and the at least one antenna; at least one waveguide
interconnecting the communication device and the signal-carrying
structure; at least one lightning receptor; at least one lightning
down conductor connected to the lightning receptor for conducting
lightning current to the root end of the blade for connection to a
ground plane; wherein the signal-carrying structure and the
lightning down conductor are short-circuited at one or more
locations within the blade.
Preferably, the at least one communication device is located within
the wind turbine blade. Even more preferably, the at least one
communication device, the at least one antenna, the at least one
signal-carrying structure, the at least one waveguide, the at least
one lightning receptor and the at least one lightning down
conductor are located within the blade.
Typically, the wind turbine blade will comprise a profiled contour
including a pressure side and a suction side, as well as a leading
edge and a trailing edge with a chord having a chord length
extending there between, the profiled contour, when being impacted
by an incident airflow, generating a lift.
The communication device will typically comprise several electronic
components such as one or more transmitters, receivers, data
processors, amplifiers and/or sensors. The mentioned components are
likely to be destroyed or damaged if lightning current enters the
communication device. It is therefore necessary to separate
lightning current from other signals entering and leaving the
communication device.
Preferably, the communication device is located as close to the
root end of the blade as technical and physical possible to
minimise impact occurring from lightning currents.
In one embodiment, the communication device comprises at least a
radio signal receiver and a data processor. This is advantageous in
that the communication device then is able to receive and process
signals from one or more of the antennas. Furthermore, the
communication device may comprise a radio signal transmitter
enabling the communication device to transmit a radio signal,
receive a radio signal and process the radio signal. The received
signal is preferably a reply from an antenna to a signal sent from
a transmitter. Such transmitter may be part of the communication
device or located external to the communication device.
In one embodiment, the communication device comprises a radio
signal transmitter, a radio signal receiver and a data processor
for processing data such as the received radio signal from an
antenna. This allows for time-of-flight measurements, e.g. to
monitor blade deflection.
The communication device may furthermore comprise a blade sensor
facilitating measuring information representing blade orientation.
Examples of information representing blade orientation could be
acceleration or speed of movement of the blade sensor and thereby
of the blade. A further example could be rotational position of the
blade sensor device in relation to the earth gravity also simply
referred to as gravity. The preferred examples of blade orientation
are blade pitch angle and blade azimuth angle.
Preferably, the antenna is an antenna suitable to broadcast an
ultra-wide band signal (UWB).
According to one embodiment of the invention, at least one of
antennas is a tip antenna located at the tip end of the blade. The
tip end of the blade is defined as less than eight meters
preferably less than one meter from the tip end of the blade.
Preferably, the one or more tip antenna(s) is located inside the
blade, alternatively such tip antenna(s) may be at least partly
moulded into the structure of the blade. Preferably, the tip
antenna is an antenna transmitting a signal to a root antenna.
According to an embodiment of the invention, at least one of the
one or more antennas is a blade antenna located between 4 meters
and 10 meters longitudinal distance from the tip of the blade.
Preferably, the blade antenna is located at a distance of around 5
meters from tip of the blade. Advantageously, the one or more tip
and or blade antenna(s) is located inside the blade. Alternatively,
the antenna(s) may be at least partly moulded into the structure of
the blade. Preferably, the blade antenna is an antenna transmitting
a signal to the root antenna.
According to an embodiment of the invention, at least one of the
one or more antennas is a root antenna located outside the blade.
Preferably, the root antenna(s) are located outside the blade at
the root end of the blade. The root end of the blade is defined as
less than four meters preferably less than one meter from the joint
between the blade and the hub of the wind turbine. Preferably, the
root antenna is spaced from the surface of the blade; hence,
advantageously the root antenna is mounted on brackets. Preferably,
the root antenna is an antenna receiving a signal from a tip and/or
a blade antenna.
Typically, the signal will be a radio frequency (RF) signal. RF
electromagnetic waves are capable of spreading through free space
as the inside of a waveguide.
The necessary separation of lightning current is obtained by
inserting a waveguide between the signal-carrying structure and the
communication device. The waveguide separates lightning current
from e.g. radio signals and facilitates that the lightning current
can be conducted away from the waveguide/communication device.
Thereby the components of the communication device are protected
from lightning currents. Advantageously, a first end of the
waveguide is connected to a communication device and the second end
of the waveguide is connected to the signal-carrying structure,
such as a coaxial cable. In this way signals between an antenna and
a communication device pass through the waveguide.
Depending on type of waveguide, one waveguide may protect more than
one communication device from lightning currents. In addition, each
electric and/or communicative connection may have one waveguide in
a 1:1 configuration.
In an advantageous embodiment, the signal-carrying structure, such
as the centre conductor and shield conductor of a coaxial cable, is
connected to the waveguide at least partly by means of soldering.
It is advantageous to fasten conductor(s) to the waveguide by means
of soldering, brazing or welding in the situations where these
conductors facilitate carrying at least part of the lightning
current. Further, it may be advantageous also to use one or more
screws to fasten at least one of these conductors, especially if
the waveguide comprises an end launcher to which the
signal-carrying structure, such as the centre conductor and shield
conductor of a coaxial cable, has to be connected.
The lightning receptor is preferably located within the tip end
region of the blade. There can be more than one receptor along the
blade and the receptor design may be chosen from a variety of
different geometrical forms including a band around the blade. The
down conductor is connected to each of the receptors and in case of
lightning strikes, the down conductor conducts lightning current to
a ground potential.
According to a preferred embodiment, the lighting down conductor is
connected to one or more receptors in the tip end region of the
blade, i.e. less than eight meters preferably less than one meter,
from the tip end of the blade. Similarly, the signal-carrying
structure may be connected to an antenna in the tip end region of
the blade. At one location, typically in the tip end region of the
blade, these conductors are short-circuited enabling lightning
current flow through the blade in each of the conductors.
The down conductor is capable of conducting currents occurring from
a lightning strike of a wind turbine blade and typically, the down
conductor is connected to a lightning receptor in one end and a
ground potential or connection hereto in the second end.
In one embodiment, the dimension of the lightning down conductor is
between 35 mm.sup.2 and 70 mm.sup.2. The dimension of the down
conductor depends on the material of the down conductor and on
whether the down conductor has to carry the entire lightning
current alone or not. In the former case, the dimension of the down
conductor is preferably 50 mm.sup.2 CU or 70 mm.sup.2 ALU or other
conducting material vs dimension that give equivalent lightning
current conduction capability. The latter case may occur if e.g.
the lightning current is also at least partly carried by a second
conductor such as the signal-carrying structure. In this case, the
dimension of the down conductor depends on the type of coax cable
and according to embodiments of this invention; the dimension of
the down conductor may be below 50 mm.sup.2.
Preferably, the short circuit is a direct current (DC) short
circuit. The short circuit between the lightning down conductor and
the signal-carrying structure is advantageous in that the connected
conductors each are carrying part of the lightning current and
thereby the dimensions of e.g. the lighting down conductor or parts
thereof may be reduced. More importantly, the short-circuit ensures
that the electric potential across the insulation of the different
conductors of the lightning down conductor and the signal-carrying
structure is low and non-destructive in case of lightning current
passing.
At the waveguide, which is typically in the root end region of the
blade, the three conductors are again preferably separated.
Typically, the signal carrying conductor(s) are connected to the
waveguide and the lightning down conductor is connected to an
additional down conductor. These connections facilitate that the
waveguide and the communication device attached hereto acts as a
"dead end" for the lightning current, which then continues to
ground or ground potential via the additional down conductor. The
communication device is usually electrically isolated/galvanically
separated from the rest of the wind turbine. The waveguide may act
as a common terminal for the lightning current conducting parts of
the lightning conductor and the additional lightning carrying
conductor.
In an advantageous embodiment, the signal-carrying structure
comprises one or more signal-carrying coaxial cables, each coaxial
cable comprising a centre conductor surrounded by a first tubular
insulating layer enclosed by a tubular shield conductor.
At least the centre conductor passes the signal between the one or
more antennas and the communication device. Coaxial cables are
preferred in situations where the conductor carries high frequency
radio signals between the communication device and the antennas in
that the coax cable design is optimised for this purpose. In one
embodiment, the tubular shield conductor is corrugated.
In one embodiment, the coaxial cable is a 50 ohm type coaxial
cable. The type of coaxial cable is preferably 50 ohm for obtaining
the best signal noise ratio when transmitting a radio signal
between 3 and 5 GHz through a blade having the length of 30 to 80
meters or more. The optimum depends on the dielectric between the
centre conductor and the shield, but is usually in the 50-70 ohm
range. Typically, the standard 50/75 ohm cables are chosen.
The signal-carrying structure may comprise several signal-carrying
coaxial cables, typically interconnected by one or more splitters
or ground returns as discussed below. Each of several antennas may
be connected to the communication device by its respective coaxial
cable via respective waveguides.
In a preferred embodiment, one or more of the signal-carrying
coaxial cables is at least over part of its length integrated into
a three-conductor cable comprising a second tubular insulating
layer surrounding the tubular shield conductor, the second tubular
insulating layer being surrounded by at least part of the lightning
down conductor.
The three-conductor cable has the advantage that it minimises the
number of cables that need to be installed in the blade. In a
preferred embodiment of such three-conductor cable, the lightning
down conductor has the form of a tubular shield or sock applied
outside the other conductors. Further it is advantageous if the
integration also includes an isolating layer outside the sock in
that electric arcs between cable an e.g. blade components then are
avoided or at least significantly reduced.
According to an embodiment of the invention, the lightning down
conductor encapsulates the conductor preferably by a sock made of a
current conducting material. Since the lightning currents are high
enough to destroy electronics and interfere with communication
signals these currents are preferably conducted from blade to
ground via a predefined lightning current path, wherein the
predefined lightning current path is conducting the current along a
path which facilitates no damage to electronics and less
interference of communication signals. Advantageously at least part
of such predefined lightning current path is a sock preferably made
of a metal encapsulating the signal-carrying conductor(s) between
the antennas and the communication device.
The metal sock is preferably made of aluminium due to the current
conducting capabilities of aluminium, but could also be made of
other materials capable of conducting current such as copper.
In one embodiment, the three-conductor cable comprises a third
insulating layer isolating the lightning down conductor, e.g. the
sock, from the surroundings. The layer of insulation outside the
sock ensures that the lightning current follows the outer sock in a
predefined lightning current path. The predefined lightning current
path typically starts at the blade tip and ends at the ground where
the foundation of the wind turbine is made.
In an alternative embodiment of the three-conductor cable, there is
no isolating layer between the shield conductor of the coax cable
and lightning conductor, such as the outer sock.
In a particularly preferred embodiment, the signal-carrying
structure comprises at least one power splitter for splitting and
transferring radio frequency power, the power splitter comprising
one input port and at least two output ports, each port being
adapted to connectively receive a signal-carrying cable, wherein
the input port is connected to each of the output ports such that a
radio frequency signal received at the input port is split to the
output ports. Preferably, the signal is split substantially equal
to the output ports. The splitter enables a radio frequency signal
transmitted from the communication device and reaching the input
port to be split and transferred to a first output port, which may
receive a signal-carrying coaxial cable leading to a blade antenna,
and to a second output port, which may receive another
signal-carrying coaxial cable leading to a tip antenna. Another
option is to have an unequal split, e.g. to pass more power to the
antenna with the longest cable and longest transmission path and
less power to the other antenna.
In another embodiment, the power splitter comprises a conductive
housing connected to the input port to enable a direct current
short-circuit of the housing and the input port. This enables
lightning current received at the conductive housing, by means of a
lightning down conductor mounted either to the housing or to one of
the output ports of the splitter to pass the splitter and to be
transferred to the input port for further transfer to ground. In
addition, by establishing a direct current short circuit the
lightning current can be distributed over all three conductors of a
three-conductor cable connected to the input port and the electric
potential difference between the conductors can be minimized.
In another embodiment, the signal-carrying structure is
short-circuited with the lightning down conductor at the power
splitter. In another embodiment, the input port and at least one of
the output ports is adapted to connectively receive the
three-conductor cable described above.
According to a preferred embodiment, the blade also comprises a
ground return for transferring radio frequency power and lightning
current, the ground return comprising an input port and an output
port, each port being adapted to connectively receive a
signal-carrying cable, wherein the input port is connected to the
output port such that a radio frequency signal received at the
input port is transferred to the output port, the ground return
having a conductive housing comprising connection means for
connectively receiving the end of a conductor connected to a
lightning receptor, wherein the ground return enables a direct
current short-circuit of the housing and the input port.
Preferably, the input port of the ground return is adapted to
receive a three-conductor cable as described above. Advantageously,
the ground return is placed within the tip end region of the
blade.
In a particularly preferred embodiment, the wind turbine blade
comprises a lightning receptor connected to the conductive housing
of the ground return, a first antenna connected to the output port
of the ground return by way of a signal-carrying coaxial cable, a
first three-conductor cable as described above connected to the
input port of the ground return, the opposing end of said first
three-conductor cable being connected to a first output port of a
power splitter as described above, a second antenna connected to a
second output port of the power splitter by way of a
signal-carrying coaxial cable, a second three-conductor cable
connected to the input port of the splitter, the opposing end of
said second three-conductor cable being connected to a waveguide,
the waveguide being connected to a communication device.
Preferably, one or two additional antennas are connected to the
communication device via respective waveguides.
In another embodiment, the blade comprises two or more antennas
placed at different longitudinal distances to the tip end of the
blade. Advantageously, the blade comprises a first and a second
antenna, the first antenna being placed within one meter
longitudinal distance from the tip end of the blade, and wherein
the second antenna is placed between four and ten meters
longitudinal distance from the tip end of the blade.
Typically, the signal is a radio frequency signal.
In another aspect, the present invention relates to a wind turbine
blade comprising a lightning protection system, the wind turbine
blade extending in a longitudinal direction parallel to a
longitudinal axis and having a tip end and a root end, wherein the
blade comprises at least one communication device located within
the blade; at least one antenna connected to the communication
device; at least one signal-carrying structure for transferring a
signal between the communication device and the at least one
antenna; at least one waveguide interconnecting the communication
device and the signal-carrying structure; at least one lightning
receptor; at least one lightning down conductor connected to the
lightning receptor for conducting lightning current to the root end
of the blade for connection to a ground plane; wherein the
signal-carrying structure and the lightning down conductor are
short-circuited at one or more locations within the blade.
In another aspect, the present invention relates to the use of a
waveguide in a lightning protection system of a wind turbine,
wherein the waveguide interconnects a communication device located
within the turbine and a signal-carrying structure connected to at
least one antenna. This enables obtaining separation of lightning
current and radio signal transferred possibly present on a
signal-carrying structure. Preferably, the communication device and
the signal-carrying structure are located within a blade of the
wind turbine. Thereby it is possible to have electronics in the
blade of a wind turbine with very little risk of damage due to
lighting current
In a preferred embodiment of the use of the waveguide, the
signal-carrying structure is short-circuited with a lightning down
conductor at one or more locations within the blade, wherein the
waveguide is used for preventing lightning current conducted by the
signal-carrying structure from entering the communication
device.
In another aspect, the present invention relates to a power
splitter for splitting and transferring radio frequency power
within a wind turbine blade, the power splitter comprising one
input port and at least two output ports, each port being adapted
to connectively receive a signal-carrying cable, wherein the input
port is connected to each of the output ports such that a radio
frequency signal received at the input port is split to the output
ports, and wherein the power splitter comprises a conductive
housing connected to the input port to enable a direct current
short-circuit of the housing and the input port. Preferably, the
signal is split substantially equal.
Preferably, the input port and at least one of the output ports is
adapted to connectively receive a three-conductor cable comprising
a signal-carrying center conductor surrounded by a first tubular
insulating layer enclosed by a tubular shield conductor, the
tubular shield conductor being surrounded by a second tubular
insulating layer, the second tubular insulating layer being
surrounded by a third conductor.
In another aspect, the present invention relates to the use of the
above-described power splitter in a lightning protection system of
a wind turbine blade.
As used herein, the term "waveguide" refers to a hollow conducting
structure, such as a hollow metal tube or metal box, suitable for
acting as a transmission line for electromagnetic waves of radio
frequency. A waveguide acts as a high pass filter allowing
electromagnetic waves above a certain cut-off frequency to pass
through the waveguide (typically radio frequency waves), whereas
most of the electromagnetic energy below the cut-off frequency,
such as lightning current, will be attenuated by the waveguide. The
cross section may have one of the following shapes: square,
rectangular, circular, elliptical, dual-ridge (H-shaped) or
single-ridge (U-shaped). The cut-off frequency, dispersion and/or
attenuation will depend on the cross-section.
As used herein, the term "substantially equal" means a power split
in which each resulting output signal is within +/-10% or the other
output signal(s).
Moreover, the invention relates to a wind turbine blade having a
predefined lightning current path, the predefined lightning current
path includes at least a lightning receptor located in the blade, a
down conductor located inside the blade and an additional down
conductor connecting the down conductor to a ground potential
characterised in that the predefined lightning current path
bypasses a waveguide. Preferably, the waveguide is located in the
blade. Preferably, the additional down conductor is connected to
the down conductor at the connection of the down conductor to the
waveguide. Alternatively, the connection of the down conductor and
the additional down conductor is isolated from the waveguide. The
conductor is preferably carrying a communication signal between an
antenna located in the blade and a communication device preferably
the antenna is located at the opposite end of the conductor than
the waveguide.
According to a preferred embodiment, the predefined lightning
current path is at least partly implemented as a sock encapsulating
a signal-carrying structure implemented as a coaxial cable in the
blade.
It will be apparent to the skilled reader, that the embodiments
discussed herein may be combined with each other.
FIGURES
A few exemplary embodiments of the invention will be described in
more detail in the following with reference to the figures, of
which
FIG. 1 illustrates a wind turbine according to an embodiment of the
invention,
FIG. 2 illustrates a blade with a radio based measuring system
according to an embodiment of the invention,
FIG. 3 illustrates a conductor according to an embodiment of the
invention,
FIG. 4a illustrates a side view of waveguide according to an
embodiment of the invention,
FIG. 4b illustrates a front view of waveguide according to an
embodiment of the invention,
FIG. 5 is schematic drawing of a lightning protections system
according to the present invention, and
FIG. 6 is a cross-sectional view of a power splitter according to
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an electrical power generating system in form of
a variable speed wind turbine 1 according to an embodiment of the
invention. The wind turbine 1 comprises a tower 2, a nacelle 3, a
hub 4 and two or more blades 5. The blades 5 of the wind turbine 1
are rotatably mounted on the hub 4 at their respective root ends,
together with which they are referred to as the rotor. The end of
each blade 5 opposite the root end is the tip end. The rotation of
a blade 5 along its longitudinal axial is referred to as pitch. The
wind turbine 1 is controlled by a control system comprising a wind
turbine controller 6, sub controllers 7 for controlling different
parts of the wind turbine 1 and communication lines 8.
FIG. 2 illustrates a blade 5 of a wind turbine 1 according to an
embodiment of the invention. The blade 5 is equipped with a radio
based measuring system comprising communication device 9 protected
from lightning currents by means of a waveguide 12, a conductor 11
and antennas 10. The communication device 9 preferably comprises at
least a radio signal transmitter 14A, a radio signal receiver 14B
and a data processor 15 for processing data including the received
radio signal (especially the time the radio signal travels from
transmitter 14A to receiver 14B is interesting to find and
analyse). The radio signal transmitter/receiver 14 could be
implemented as one device capable of both sending and receiving.
The communication device 9 could also include additional elements
such as e.g. a blade sensor 16 in the form of accelerometer and/or
gyroscopes, etc.
The communication device 9 is communicating with the rest of the
wind turbine control system 6, 7 preferably via optical
communication means such as an optical fibre 8 connected to a data
communication interface 26.
The communication device 9 is preferably powered via a power supply
interface 27, which is galvanic insulated from the rest of the
communication device 9.
The communication device 9 preferably transmits a radio signal via
a tip antenna 10A, which is illustrated at the tip of the blade 5.
The radio signal is received by one or more root antennas 10C
placed near the root end of the blade 5. A further transmitting
blade antenna 10B may also transmit a radio signal. Radio signals
from additional (not illustrated) antennas could also be provided
to/from the radio signal receiver/transmitter 14 of the
communication device 9.
A radio signal-carrying conductor 11 is connected to the antennas
10. The conductor 11 is at the other end connected to a waveguide
12, which at the other end is connected to the communication device
9. In a preferred embodiment of the invention the radio
transmitting device 14A is transmitting via waveguide 12 and
conductor 11 a radio signal to the tip antenna 10A and if any
preferably also to the blade antenna 10B. The tip antenna 10A
transmits (transmit may in this application be interpreted as
broadcast or communicated) the radio signal which is then received
by one or more root antennas 10C and transmitted to the radio
signal receiver 14B of the communication device 9. In alternative
embodiments, the radio signal is transmitted from the blade
antennas 10C to the tip antenna 10A/blade antenna 10B and via the
conductor 11 and waveguide 12 to the communication device 9.
It should be noted that in an alternative configuration each of
antennas 10C could be connected to separate waveguides 12.
FIG. 3 illustrates the same type of conductor 11, 13 differently.
The conductor 11, 13A, 18 between the waveguide 12 and the splitter
30 is illustrated by displaying the different layers of the
conductor 11, 13A. The same is the case for the conductor 11, 18
from the splitter 30 to the blade antenna 10B just with less
layers. The conductor 11, 18 from the waveguide 12 to the root
antennas 10C is simply illustrated as a single line but are
implemented as a multi-layered conductor as the above mentioned.
The conductor 13B is preferably a standard down conductor with or
without isolation layer. This different way of illustrating the
conductor 11, 13 is simply to illustrate that it may be implemented
differently i.e. the number of layers are not necessary the same in
the entire blade depending on the purpose of the conductor cable.
The conductor 11 is preferably implemented as a type of cable,
preferably a coax cable 18.
It should be mentioned that if only one receptor 17 is located in
the blade 5 it is preferred that a not illustrated second isolation
layer 20 is applied outside the sock 19.
The waveguide 12 comprises an end launcher 22 to which the signal
carrying conductor 23 is connected as described in relation to FIG.
4B.
The waveguide end launcher 22 is preferably a step type of end
launcher 22 to which the inner conductor i.e. the signal-carrying
conductor 23 of the radio signal carrying conductor 11 is
connected. The end launcher 22 may as illustrated on FIG. 2 be
implemented as one or more steps where the inner conductor 23 of a
coax cable conductor 11, 18 is mounted. It should be mentioned that
waveguides 12 without an end launcher 22 or with other
implementations of end launchers 22 may also be used as lightning
protection of the communication device 9. It is preferred to
connect the coax cable to the end of the waveguide. An alternative
solution is to connect the coax from the top of the waveguide to
the "staircase" illustrated in FIG. 2 (element 22).
Preferably, the conductor 11 is a coax cable 18 but other types of
radio signal carrying cables may also be used.
The communication device 9 may process the received information by
means of the data processor 15 and pass the information further on
via communication line 8 to a controller 6 or sub-controller 7.
Alternatively, the information may also simply be passed through
the communication device 9 to be processed at a controller 6 or
sub-controller 7. The processing of information could include
analysing time between transmitting and receiving the radio
signal.
The communication device 9 may be powered by a power supply
interface connected by a power cable to a power source preferably
located in the hub 4.
One way of defining a lightning current is as a 200 kA pulse rising
in 10 us and reduced to 50% after 350 us. A current pulse of this
size may be very damaging to electronic equipment and disturb data
communication/radio signals in general. Therefore, the
communication device 9 has to be bypassed by such current pulse to
avoid damage of components of the communication device 9.
Especially when the communication device 9 is located in the blade
5, it needs to be protected from high currents resulting from a
lightning striking the blade. Therefore, a lightning protection
system is implemented in the blade 5. At least one lightning
receptor 17 is located in the blade 5 preferably towards the tip of
the blade 5. This lightning receptor 17 is connected to a down
conductor 13A conducting the lightning current from the receptor 17
down through the blade 5.
Preferably, a splitter 30 is located at the end of the conductor 11
where one or more of its conductors 23, 25 are short-circuited with
the outer sock 19 constituting the down conductor 13A. In this way,
all conductors of the conductor 11 participate in conducting the
lightning current. From the splitter 30 receptors 17 and antennas
10 is connected.
According to an embodiment of the invention, the down conductor 13A
is implemented as an outer sock 19 preferably of metal, which is
covering or encapsulating the radio signal conductor 11. This is
advantageous in that only one cable then needs to be mounted
throughout the blade. To protect the communication device 9 the
conductor 11 and down conductor 13A are terminated in one end at
the waveguide 12. This termination enables the radio signal from
the antennas 10 to continue via the waveguide 12 to the
communication device 9. At the same time, the down conductor 13 is
bypassing the waveguide 12 and continues the electric path from the
receptor 17 via an additional down conductor 13B towards a ground
potential.
The connection between the conductor 11 and the waveguide 12 is
preferably made by means of soldering, brazing, welding or the
like. Alternatively, a plug is mounted on the conductor 11 which
fits a socket located at the waveguide 12 such plug should
preferably comply with demands to plugs handling lightning
currents. The down conductor 13A bypasses the waveguide 12, hence
the down conductor 13A and the additional down conductor 13B are
connected and the additional down conductor 13B conducts the
lightning current further towards a ground potential round the
waveguide 12.
According to an embodiment alternative to the above embodiment
having separate inner signal carrying conductor 23 and outer sock
19 also referred to as metal sock 19 the blade measuring system may
comprise a conductor 11, 13 where the inner signal carrying
conductor 23, outer conductor 25 and metal sock 19 are
short-circuited. In this way, the energy from a lightning striking
a receptor 17 is conducted through the blade 5 partly in the signal
carrying conductor 23, partly in the outer conductor 25 and partly
in the metal sock 19.
According to this embodiment, then at the joint between the
communication device 9 and the conductor 11, 13 the inner conductor
23, outer conductor 25 and metal sock 19 is again short. As
described the inner conductor 23 is preferably guided to the
interior of the waveguide 12 where it may be connected as described
above. An additional down conductor 13B is preferably attached to
the point of short circuit and thereby conducting the lightning
current further around the communication device 9. In this way, the
inner conductor 23 is short via the end launcher 22, which is
conductively connected to the waveguide 12. Thereby the lightning
protection is created in that the lightning current sees a short
and bypasses the waveguide via conductor 13B and the radio signal
is transformed between a wave in the coax and a wave in the
waveguide.
In case of more than one lightning receptor 17, the conductors of
the down conductor 13 and conductor 11 may be short at each
lightning receptor 17. With this said it is preferred that only one
receptor is used in the blade 5.
As mentioned the waveguide 12 separates the lightning current from
the radio signal, the conductor 11, 13 and the communication device
9 "floats" at the same potential present at the junction between
the conductors 11, down conductor 13 (preferably implemented as a
sock 19, but could also be a separate cable) and waveguide 12. To
obtain this floating potential of the communication device 9 it is
preferred that the power supply and data communication to the
communication device 9 is galvanic isolated from rest of the wind
turbine. This could e.g. be obtained by the use of optic fibres and
galvanic isolated connections to the communication device 9.
As indicated on FIG. 2 the communication device 9 is not limited to
transmit, receive and forward a received (e.g. processed) signal.
In embodiments of the invention, the communication device 9 also
comprises one or more blade sensors for evaluating blade
orientation such as pitch angle, azimuth angle, rotor speed
etc.
Hence by using one or more waveguides as part of the signal passage
from radio to antennas and vice versa the lightning related energy
e.g. represented by a current is separated from the sensitive
signals, radio and other electronic components.
FIG. 2 illustrates one tip antenna 10A, one blade antenna 10B and
two root antennas 10C connected to one communication device 9 via
conductors 11 and a plurality of waveguides 12. It should be
mentioned that more antennas 10, conductors 11, communication
devices 9 or waveguides 12 may be used if necessary even though not
illustrated on FIG. 2. Also the relationship between conductors 11
and waveguides is preferably 1:1.
The antenna 10A illustrated closest to the tip end of the blade may
also be referred to as tip antenna, the antenna 10B illustrated
between the tip antenna 10A and the communication device 9 may be
referred to as blade antenna 10B and the antenna located at the
blade root may be referred to as root antenna 10C.
Furthermore, FIG. 2 illustrates part of a predefined lightning
current path 21 from the tip end of the blade 5 to ground. The part
illustrated on FIG. 2 is the part of the predefined lightning
current path starting at the receptor 17 at the tip end of the
blade 5 to an additional down conductor 13. Through the blade 5 the
predefined lightning current path bypasses a waveguide 12 connected
to a communication device 9, which is thereby also bypassed.
FIG. 3 illustrates an example of a conductor 11, 13 that is used to
carry both radio signal to/from the antennas 10 and the lightning
current from the receptor 17. The illustrated example is a coax
cable 18 comprising a centre radio signal-carrying conductor 23,
first isolating layer 24 and an outer conductor 25. These layers
are typical layers of a coax cable 18. Such coax cable 18 may also
be used as conductor 11 for communication between root antennas 10
and the communication device 9 and between splitter 30 and antennas
10.
On top of the outer conductor 25 a coax cable isolation layer 29
may isolate the coax cable 18 from the metal sock 19 which is
intended for at least partly carrying the lightning currents
through the blade in case a lightning strike. On top of the metal
sock 19, an isolation layer 20 may be placed to limit risk of such
lightning current "jumps" to other blade components instead of
staying in the conductor 11, 13, 18.
The outer sock 19 may be configured with one or more layers (not
shown) between the metal and the isolation layer 20. These one or
more layers may comprise fabric or polymeric material and may be
semi-conductive having a conductivity between the conductivity of
the metal and the isolation layer 20.
Both the coax cable isolation layer 29 isolating the coax cable 18
from the metal sock 19 and the second isolation layer 20 isolating
the metal sock 19 from the surroundings are optional. Hence, in
some embodiments of the invention the conductor 11, 13 may only
comprise an inner radio signal-carrying conductor 23, first
isolating layer 24 and an outer conductor 25. With this said in
some configurations where only one receptor 17 is placed in the
blade the sock 19 and the second isolating layer 20 is
recommended.
Hence by including the antenna system of a blade measuring system
in a faraday cage construction such as a metal sock 19 as part of
the lightning protection system it is ensured that the lightning
energy (also referred to as lightning current) is passed around the
antenna system. The antenna system may comprise the antennas 10,
conductor 11 and communication device 9.
There are different types of waveguides for different types of
waves and the preferred according to this invention is a hollow
conductive metal pipe such as the one illustrated in a side view on
FIG. 4A. The waveguide 12 may in addition have flanges (not
illustrated) for fastening the waveguide 12 e.g. to the
communication device 9. Such flanges may also be used for fastening
the outer conductor 25 of the conductor 11 to the waveguide 12. In
embodiments the outer sock 19 may also be fastened to such flange
and thereby create a short between the outer conductor 25 and the
outer sock 19. Alternatively, such short could be facilitated by
terminating the outer conductor 25 and the outer sock 19 in a
terminal or soldering which is galvanic connected to the waveguide
12. The waveguide 12 is preferably connected by a conductor 11 to
the communication device 9 but may also be attached to directly to
the communication device 9.
FIG. 4B illustrates an end view of the waveguide 12. The
signal-carrying conductor 23 is preferably terminated in a terminal
28, which is part of the end launcher 22, which is connected to the
waveguide 12. Hence for the a lightning current the outer conductor
25, outer sock 19 and signal carrying conductor 23 is short via the
end launcher 23 and waveguide 12. This is in contrast to the GHz
radio signal which faces a 50 ohm resistance hence protection from
lightning current is obtained.
It should be mentioned that the end launcher 22 may be implemented
as a small antenna inside the waveguide 12 or the like. Further, it
should be mentioned that the two end launchers 22 of the waveguide
does not necessarily have to be of the same type.
A suitable waveguide 12 for a 3-5 GHx radio signal could be
approximate 30.times.60.times.300 millimeters (H.times.W.times.L).
The dimension of the waveguide 12 is determined based on the radio
frequency which is used. Appropriated frequencies according to
embodiments of the present inventions may e.g. be from 3 to 5 GHz
or even higher.
FIG. 5 is a schematic drawing of a lightning protection system 31
according to the present invention. It shows a communication device
9 connected to a tip antenna 10a, a blade antenna 10b and two root
antennas 10c, 10d. A three-conductor cables 18a comprising a
signal-carrying centre conductor, a coaxial shield and an outer
sock, is arranged between waveguide 12a and splitter 30. The
splitter 30 is further described below with reference to FIG. 6.
Another three-conductor cable 18b interconnects the splitter and a
ground return 32, the latter being connected to a lightning
receptor 17 and to the tip antenna 10a. The purpose of the ground
return 32 is to conduct the lightning current originating from the
lightning receptor on its conductive housing to the three-conductor
cable 18b, the ground return 32 providing a direct current
short-circuit between the three conductors of cable 18b. Also, the
ground return 32 transfers a radio signal originating from the
communication device 9 to the tip antenna 10a. Each antenna is
connected with a coaxial cable.
FIG. 6 is a schematic cross-section of a power splitter 30
according to the present invention. It has an input port 33 for
connectively receiving a three-conductor cable, and two output
ports 34, 35. The output port 34 is also adapted to connectively
receive a three-conductor cable. The outer sock of the cable, i.e.
the lightning down conductor 19, is clamped to the input port 33 by
means of clamp 41 such that the sock is connected to the conductive
housing 36 of the splitter 30. The other output port 35 is adapted
to receive a signal carrying coaxial cable with a center conductor
and a coaxial shield, the cable leading to an antenna. The power
splitter 30 has a conductive housing 36 for transferring lightning
current originating from the tip end, i.e. for output port 34, to
the root end, i.e. input port 33. Conversely, a radio signal
transmitted from the communication device is received in input port
33 and split within the device substantially equally to the output
ports 34 and 35 by way of the inner conductors 37, 38, 39 being
connected via the conductive staircase 40.
It will be understood by the skilled reader that the
above-described embodiments are of exemplary nature only, and that
other alternatives of implementing the present invention are
conceivable.
LIST OF REFERENCE NUMBERS
1. Wind turbine 2. Tower 3. Nacelle 4. Hub 5. Blade 6. Wind turbine
controller 7. Sub controller 8. Communication line 9. Communication
device 10. Tip antenna (10A), Blade antenna (10B), Root antenna
(10V) 11. Conductor 12. Waveguide 13. Down conductor (13A),
Additional down conductor (13B) 14. Radio signal transmitter (14A),
Radio signal receiver (14B) 15. Data processor 16. Blade sensor 17.
Lightning receptor 18. Coax cable 19. Outer sock 20. Second
isolation layer 21. Predefined lightning current path 22. End
launcher 23. Signal carrying conductor 24. First isolating layer
25. Outer conductor 26. Data communication interface 27. Power
supply interface 28. Terminal 29. Coax cable isolation layer 30.
Splitter 31. Lightning protection system 32. Ground return 33.
Input port 34. Output port 35. Output port 36. Housing 37. Centre
conductor 38. Centre conductor 39. Centre conductor 40. Copper
staircase 41. Clamp
* * * * *